1. Past continuous
was / were + V_ing

2. We use the past continuous tense to describe a period of time in the past.

3. Compare the past continuous (I was doing) and past simple (I did):
Past continuous (in the middle of an action)
I was walking home when I met Dave. (in the middle of walking home)
Ann was watching television when the phone rang.
I was sitting in class when I fell asleep.
We were talking when the teacher came into the room.
They were having lunch in the park when it started to rain.

4. GRAMMAR
I was
You were
He / She / It was V_ing
We were
They were

5. Tom burnt his hand when he was cooking the dinner.
Past simple and past continuous are used together when something happened in the middle of something else.
Tom burnt his hand when he was cooking the dinner.
I saw you in the park yesterday. You were sitting on the grass and reading a book.
While I was working in the garden, I hurt my back.

6. But we use the past simple to say that one thing happened after another:
Compare:
When Karen arrived, we were having dinner (we had already started dinner before Karen arrived).
When Karen arrived, we had dinner. (first Karen arrived and then we had dinner)

7. There are some verbs (for example, know/want/believe) that are not normally used in the continuous:
We were good friends. We knew each other well (NOT “we were knowing”).
I was enjoying the party but Chris wanted to go home.